A structure and method for bonding heat-insulating protection walls of a liquefied natural gas carrier is provided. Each of the heat-insulating protection walls is formed of an insulation foam layer and a fiber-reinforced composite reinforcing sheet attached to a surface of the insulation foam layer. The heat-insulating protection walls are provided in a tank of the liquefied natural gas carrier in a mutually adjoining relationship and bonded to one another at a junction to keep the tank cold. The structure includes a fiber-reinforced composite joint sheet positioned in alignment with the juncture of the heat-insulating protection walls and bonded to the fiber-reinforced composite reinforcing sheet by an adhesive agent and a spacer interposed between the fiber-reinforced composite reinforcing sheet and the fiber-reinforced composite joint sheet for keeping the adhesive agent uniform in thickness.